I have the area outlined - I need all of the air blocks from sea level up to 71 turned into dirt. A few hills will stick up above, but that's okay as they will seed in the grass. If the hills are in the park area I'll incorporate them into the design. Here are the coordinates of the four corners:
___________ N
-379___________________ -29
71_____________________ 71
-378___________________ -378
W______________________ E
-379___________________ -29
71_____________________ 71
-27____________________ -27
____________ S
That's about 350 blocks on a side, which is 10 more than I need which should make it easier for me to blend the edge in with the landscape. My first job will be to light everything up with a torch grid so that I can work safely through the night. I will be building a giant sequoia in the very center of the park. There will be a room inside the base of the tree in which will be the portal - which will be the only way in or out of the city. I'll post reminders not to remove anything. I'll also build a petition board where players can ask Loki for materials to build things. Most of the city should be visible from the giant sequoia, though of course the top will be too high to see the ground - there will be small observation platforms on lower branches.
I would also like to ask Loki if I could have several stacks of redwood/rainforest logs - a full double chest even, as that sequoia is going to take a lot and I really don't want to chop down the rainforest

No materials used in the city will be taken out into the rest of the map.